Well technology constantly develops, and the smart completion technology has traditionally been in focus. However, changes need to be made to a well during its lifetime in order to optimise production, and these changes are not always predictable and can thereby not be taken into account when assembling the casing. One necessary change could be machining an opening in the casing in order to insert a control valve to initiate gas lift. Another change required could be to machine a larger opening in the casing in order to make a side track. However, when making larger holes, elongated holes or just holes different from the size of the bit, the machining technology CNC from sub surface cannot be used as this technology requires a lot of space and power which is limited downhole.